The incorporation of active ingredients inside nano-sized systems has helped to solve formulation constraints of these molecules, further increasing their therapeutic potential. Improvements in solubility, protection against degradation or increased penetration of the active ingredients are some of the advantages of active molecule nanoencapsulation. Likewise, it is also known that the capacity of these systems to cross external barriers and access the interior of the organism, both depends on their size and on their composition. Small-sized particles will increase the degree of transport with respect to those of larger size: nanosystems, with a diameter of less than 1 μm, meet this criteria.
Polyglutamic Acid (PGA)
Polyglutamic acid (PGA) is a hydrophilic and biodegradable polymer made of negatively charged glutamic acid units. Due to its biological properties such as non-toxicity, its non-immunogenicity and biocompatibility, this polymer has been regarded as an important biomaterial for the development of new formulations for drug delivery (Buescher & Margaritis, Crit RevBiotech 2007).
For example, the use of polyglutamic acid is widely reported for the formation of drug-polymer complexes of interest in cancer treatment, being some formulations in advanced development stages. Such is the case of Xyotax, a formulation consisting of conjugates between poly-L-glutamic acid and cytostatic agent paclitaxel, which is currently in Phase 3 clinical trials. Also this polymer has been used to design formulations for administering other antitumor agents such as doxorubicin (Shih et al., 2004).
Furthermore, US 2006/0246096 reports the use of polyglutamic acid in the formulation of drug delivery systems, being used as shell in formulations for the carrying genetic material from them.
Another type of delivery system developed from polyglutamic acid are the nanoparticles, as disclosed in US 2005/0238678 and U.S. Pat. No. 6,326,511.
On the other hand, polyglutamic acid has also been conjugated to polyethylene glycol (PEG) in order to effect changes on the surface of nanometric systems, attempting to provide greater stability of colloidal systems. Such modification with PEG also minimizes recognition of nanosystems by proteins and cells of the reticuloendothelial system, thus increasing the circulation time thereof.
The effect of conjugation of the PEG with polyglutamic acid has been investigated in US 2003/0170201, which assesses the potential of the complexes formed from such polymer for releasing of cytostatic drugs.
Hyaluronic Acid (HA)
Hyaluronic acid (HA) is a naturally occurring polymer. More specifically it is a glycosaminoglycan present in the extracellular matrix of connective tissues such as the subcutaneous and cartilaginous; it is also found in the vitreous body of the eye and synovial fluid of articular cavities. It is a polymer capable of interacting with CD44 and RHAMM endogenous receptors which are located at the cell surface in practically all cells of the body except red blood cells. The interaction of hyaluronic acid with these receptors allows regulating certain physiological processes such as mobility and cell proliferation. Due to these properties, hyaluronic acid has therapeutic use, as it plays an important role in processes such as morphogenesis and embryo development, cancer and inflammation. Moreover, due to said properties, hyaluronic acid is used to promote epithelial healing. Proof of this biological activity are numerous jobs that include hyaluronic acid as active biomolecule, were we can mention those described by Sand et al. (Acta Ophthalmol. 67, 1989, 181-183), where hyaluronic acid is applied in the treatment of keratoconjunctivitis sicca, by Nishida et al. (Exp. Eye Res 53, 1991, 753-758), wherein it is applied to corena as healing agent and by Blanco et al. (Clin. Exp Rheumatol. 22 (3) 2004, 307-12), where the polymer is applied for the treatment of osteoarthritis, among others. Additionally, hyaluronic acid and its derivatives, under various forms of presentation, have been the subject of numerous patent documents wherein they are presented as active molecules. At this point it should be noted patent application WO 96/06622, which claims the use of hyaluronic acid and derivatives, alone or in combination with another therapeutic agent, to modulate cellular activity of those tissues and cells which express on their surface hyaluronic acid receptors, and thus treat or prevent inflammatory processes, fibrosis or oncogenesis. U.S. Pat. No. 6,383,478 protects a delivery system consisting of microparticles, nanoparticles or films which incorporate hyaluronic acid as possible active molecule to promote angiogenesis.
On the other hand, hyaluronic acid has also been the subject of numerous studies proposing its use as a biomaterial-excipient used in the development of drug delivery systems. The interest is due to the fact that it is a biodegradable polymer, biocompatible, non-immunogenic, mucoadhesive and selective affinity for receptors such as CD44. Regarding the antecedents focused on obtaining nanometric formulations using hyaluronic acid as biomaterial-excipient the following, among many other, can be mentioned:                U.S. Patent Application 2007/0224277, which describes the preparation of hyaluronic acid nanoparticles formed by covalent crosslinks.        U.S. Patent Application 2003/0166602 A1, which discloses the preparation of different formulations with a hyaluronic acid-modified lipid, and that can hold active ingredients with anticancer activity or other therapeutic or diagnostic agents.        Patent Application WO 2004/112758 A1, which describes the preparation of nanoparticles in an aqueous medium containing hyaluronic acid which are formed by ionic interaction between the same, other polymers of complementary charge and in the presence of the ionic type crosslinking agent.        Luo and Prestwich (Bioconjugate Chem 10, 1999, 755-763) synthesized a conjugate between hyaluronic acid and the anticancer agent Taxol, and whose cytotoxic activity is higher and more selective than that obtained only with Taxol in breast, colon and ovarian cell lines over expressing the receptor CD44.        Yenice et al (Experimental Eye Research 2008, 87 (3), 162-7) and Barbaultfoucher et al (Journal of Controlled Release 2002, 83, 365-375) describe nanospheres of poly-ε-caprolactone coated with hyaluronic acid as system for ocular drug delivery.Polyasparagine (PAsn)        
Since it intervenes directly in the synthesis of proteins and DNA, and the main source is in the diet, L-asparagine is described in the literature as an essential amino acid for growth and development of all cell types.
L-asparagine is currently one of the more and better used strategies for cancer treatment, being commercialized a formulation that includes the enzyme required for its degradation. When administering this enzyme and achieve its deposition in the tumor periphery, a reduction in the concentration of the amino acid is obtained, causing deficiencies thereof; the cells are then prevented from synthesizing DNA and other proteins essential for survival. Such formulation is called Oncaspar™ or Elspar™, L-asparaginase being the enzyme responsible for this degradation.
Cancer cells in advanced stages of metastasis, especially leukemia, exhibit high affinity for asparagine due to a high recognition in the surface, caused by their rapid reproduction. Cancerous cells cannot effectively meet their basic needs for this amino acid, which in many cases leads to the migration of these cells in search for higher concentrations of this amino acid towards the tumor periphery. Such recognition and necessity has been recently used as an alternative for the treatment of many cancers metastatic stage. There have been numerous studies based on asparagine of nanoscale systems such as polymeric micelles or liposomes coated polymeric derivatives.
Said studies have shown great potential for the development of nanosystem based on polyaminoacids based on asparagine, such as polyasparagine (PAsn) or polyhydroxyethylasparagine. Moreover, combined with the specificity conferred by the surface recognition asparagine, polymers based on this aminoacid have shown, structural and physicochemical properties similar to PEG, which provides the drug an improved half-life in progress, and a remarkable improvement in pharmacokinetics and biodistribution.
In studies related to polyasparagine, Storm and colleagues (Metselaar, Bruin et al. 2003; Garcion, Lamprecht et al. 2006; Romberg, Kettenes-Van Den Bosch et al. 2006; Romberg, Metselaar et al. 2007; Romberg Oussoren et al. 2007; Romberg Oussoren et al. 2007; Romberg Oussoren et al. 2007; Romberg, Flesch et al. 2008; Romberg, Hennink et al. 2008) evaluated the pharmacokinetics of two different types of liposomes coatings by varying the coating polymer, comparing polyhydroxyethylasparagine with PEG. The results favored polyhydroxyethylasparagine presenting better pharmacokinetics and a longer circulation time at low doses and repeated administration.
From the information presented above, the potential and interest of the aforementioned compounds—polyglutamic acid and its copolymer with PEG, hyaluronic acid, and polyasparagine—as biomaterial-excipient in the development of new delivery systems is evident. Particularly, it would be desirable to obtain certain applications of stable nanosystems, suitable to encapsulate and protect molecules of different characteristics, and which would also present good adsorption and internalization properties into the desired biological surfaces.